Reverberations modulator



Jul 2, 1946. M, PARBIER 2,403,231

REVERBERA'I'IONS MODULATOR Filed Jan. 7, 1944 2 Sheets-Sheet 1 Fl G. 138 36 34 53 29 37 Mug/c5 .PA Ava/ER INVENTOR ATTORNEY Patented July 2,1946 BEVERBERATIONS MODULATOR Maurice Parlsier, New York, N. Y.Application January 7, 1944, Serial No. 517,321

Claims. (01. 179-1) My invention relates to sound conditioning for radiotransmission and has particular reference to sound conditioning by meansof acoustic reverberation chambers in which the sound is electricallyreproduced, conditioned, and further transmitted for broadcasting orrecording.

It is well known fact that quality of sound such -as music depends to aconsiderable-extent on the particular properties of the space, forinstance, a hall in which the sound is produced. The sound is repeatedlyreflected from the walls, producing a more or less lasting effect ofreverberation which aflects the characteristics of the sound.

For obtaining the best acoustic results, music halls are usuallyspecially designed to produce a uniform pleasing-effect of reverberation(without objectionable echo, however).

It has been found, however, that the particular type of a confinedspace, such as a hall, while it may be very effective for certain kindsof sound, for instance, for violins or chamber music, may beunsatisfactory for other kinds of sound, such as produced by windinstrument, organ, singing, etc, a

The reverberation effect depends on the physical dimensions of theconfined space or hall, and to a considerable extent, on the surface ofits walls, being difierent for smooth and rough surfaces, metal or wood,etc. Fabric (such as curtains) also considerably change the acousticproperties.

Reverberation effect is produced when a standing wave of sound isobtained in a confined space. When the sound is stopped, each individualmode of vibration will decay exponentially, and the combined eflect ofthe reverberation may be expressed by the formula:

' where V is volume of the room in cubic centimeters, a is a total roomabsorption=(A'a'+ A2a2+ A, A2 being areas in square centimeters, havingcoeflicients of absorption a, a2, etc.

It has been found that a hall, built to obtain the best results for oneparticular type of sounds, may not be satisfactory for other sounds, Ahall, suitable for sounds of low frequencies, may be entirelyunsatisfactory for sounds of high frequencies. For the best results inthe sound transmission by radio, it is necessary therefore to find meansto change the reverberation properties of the room in accordance withthe variations in the types of sound.

Proper control of reverberation is particularly important in radioindustry, for producing and recording music, speech, singing, etc.,modulating the sound to suit particular requirements, so as to producenatural and most pleasing effects.

My invention has for its object to, provide means and method of soundtransmission whereby the reverberation effect is produced artificially,by means of a chamber in which the sound is reproduced electrically andretransmitted also electrically after it has been modified acousticallyin the chamber. The chamber or enclosure is so, constructed that itsacoustic and. reverberationproperties can be rapidly changed at will,even during transmission of the sound. The chamber for this purpose isprovided with movable or collapsible walls which can be operated at adistance, by an electric motor, for instance, for causingthe walls tocollapse or to expand for varying the volume of the enclosure. Forvarying the other factor of the reverberation, i, e. sound-reflectingproperties of the walls, the walls are made re-v placeable. operated byan electric motor, for instance, at a distance, so that one particularset of walls can be quickly replaced by another set, having differentkind of surface. A plurality of telescopic walls may be provided forthis purpose or, preferably, the walls may be made of a suitableflexible material, such as fabric, plastic, etc., mounted on rolls fromwhich it can be stretched along the sides of the chamber. Differentportions of the flexible material may have different finish or may beeven made of different materials.

I have found that for the purpose of imparting particular acousticproperties to the sound by means of an adjustable acoustic reverberationchamber forming a part of a, sound transmission system, such a chambermay be of relatively small dimensions.

With proper adjustment, it is possible to obtain with such a smallchamber the eflect of the sound as produced in a large concert hall, inan open space, etc. 7

A single artificial reverberation chamber may not be satisfactory,however, for transmitting mixed sounds in which sounds of widelydifferent frequencies are used as, for instance, in the orchestralmusic, operas, singing, etc. Another object of my invention is,therefore, to provide means for independent conditioning of the soundsof different frequencies. I transmit for this purpose by electricalmeans through a series of acoustic reverberation chambers, each chamberbeing adapted to receive electric impulses corresponding to a particularband of frequencies. Each chamber is adjusted for producing the dethedesired final acoustic effect.

. ing reverberation chamber. are then recombined; means being providedto thereby.

Another object of my invention is to modify individually the volumes ofthe different bands of sound frequencies and to recombine these bandsinto a single transmission channel for obtainin For certain purposes itmay be desirable to separate the sound into two main channels fortransmission, one portion of the sound being directly transmittedthrough regular microphones and amplifiers, the other portion beingseparated into different bands of frequency, each band being thenseparately conditioned in a correspond- The two portions adjust thevolume or amount of energy in each portion (and in each band) prior totheir being combined together. The first portion, however, may be alsodivided into bands.

My invention is more fully described in the accompanying specificationand drawings in which- Fig. l is a sectional elevational. view of mysound conditioning or reverberating chamber or enclosure;

Fig. 2 is a vertical sectional view of the same taken on the line 2-2 ofFig. 1; v Fig. 3 is a sectional elevational view of a modifled chamber;a

Fig. 4 is a diagram of connections of a radio transmission of sounds inwhich a series of my sound conditioning chambers is employed;

Fig. 5 is a fractional diagrammatic view of one group of reverberationchambers; and

Figs. 6 and 7 are diagrammatic views of modified acoustic chambers.

My reverberation chamber or enclosure l for sound conditioning, a shownin Figs. 1 and 2, in one of its practical embodiments, consists of aframe, preferably of a rectangular form, made of longitudinal bars 2,attached at the ends to end walls 3, 4. These walls are stationary inthe present instance and carry electrosonic conversion means, the wall 3supporting a loud speaker 6 of an ordinary suitable type, and the wall 4supporting a microphone I, also of a suitable ordinary type. The framemay be of relatively small dimensions. Brackets 8, 9, l0, H are mountedat the ends of the frame for shafts I2, l3, I4, l5 at one end of theframe and shafts l6, l1, l8, at the other end. (The fourth shaft is notshown in the drawings.) The shafts mount rolls of a flexible sheetmaterial I9 such as fabric, plastic, thin sheet metal, etc., thematerial being stretched between the end rolls, forming walls of theenclosure I. The shafts I2, l3, l4, l5 are provided with bevel gears 22at the ends, meshing with ears 23, and one of the shafts is alsoprovided with a sprocket 24 connected by, a chain 25 with a sprocket 26on the shaft of a motor 28. The shafts I6, l1, and H3 at the other endof the frame are provided with spiral clock springs 29 which keep thesheet niaterial under tension causing the motor to turn in one or theother direction, it is possible to wind the sheet material on one set ofshafts, unwinding from the other, and to reverse the process byreversing the motor rotation. Each sheet consists of sections made ofdifferent materials, each section being of one particular material orhaving a particular'flnish.

The length of each section corresponds to the length of the frame. It ispossible, therefore, by moving the sheets in one or the other directionto bring desired sections of the sheets over the sides of the frame,thereby forming a chamber with desired acoustic or reverberatingproperties. I have found that by changing the material of the walls ofthe reverberation chamber it is possible materially to change thequality orcharacter of the sound which is being transmitted by theradio.

The character of the sound or its'reverberation is also ailfected by thevolume of the chamber. I provide for this purpose means to vary thevolume at will, controlling from a central point both the type ofthewalls and the volume of the chamber.

Forchanging the volume of the chamber, rolls 30 are provided at the mainframe on shafts 3| hearing against the sheet material. The shafts areconnected together by bars 20 and are. provided with braces 32,pivotally connected at 33 to levers 34, 35. The latter are pivoted at 36to the brackets 8, 9 at one end of the frame, the other ends of thelevers being connected together by bar 21 with nuts 31 engaging screws38, 39 having right and left thread and rotated by a motor 40. Byenergizing the motor for rotation in one or the other direction, it ispossible to move the levers together or apart, thereby compressing orreleasing the walls.

As an additional arrangement for modifying reverberation properties ofthe chamber, I provide means to change the relative angular positions ofthe loud speaker and of the microphone. These instruments are mountedfor this purpose on pivots 4|, 41 and are operated by small motors 52,i3.

A modified reverberation chamber is shown in Fig. 3. A frame 42 isslidably mounted inside a long tubular enclosure 44, the walls of theenclosure forming walls of the reverberation chamher, having a loudspeaker 6 and a microphone 'l on the end walls 45 and 46. The tubularenclosure comprises sections, having different finish of their wallsmade of different materials. The frame 42 can be moved into any desiredsection by a motor 48, driving a belt 49, mounted on pulleys 50, 5|, theends of the belt being attached to the frame 42, the return portion ofthe belt passing through suitable holes in the end Walls 45, 46.

My acoustic reverberation or sound conditioning chamber can be used forimparting any desired quality to the sound transmitted by radio as forbroadcasting, recording, etc. Thus it is possible to modulate the soundof a musical instrument or orchestra to create an impression that themusic is being played in an open space, in a large hall, in a smallroom, etc.

A single reverberation chamber, however, does not produce entirelysatisfactory result for the reason that sounds of different frequencydifferently respond to the conditioning in a particular acousticreverberation chamber. It is desirable,

therefore, to separate the sound into several through an amplifier 55into' bus bars 56. One

portion of the total electric energy of the sound is transmitteddirectly throush an manner .01.

moans:

line 58, amplifier II, to theamplifier-mixer l0. The other portion ofthe sound energy is divided into different frequency bands, passingthrough amplifiers 8|, 82,13 and through'reverberation chambers 68, 61,88, from which the electric impulses are collected by bus'bars l8 andconduct- [various changes and further modifications may be made withoutdeparting from the spirit and ed to an amplifier 10 and to themixer-amplifier 60. Potentiometers H, 1!, II, M are provided to regulatethe relativeamounts oi enersy passing through the difl'er'ent branchesof the transmission system.- Similar potentiometers 15,18.

11 are provided at the amplifiers I and II, and for the amplifier B0.

Separation of the sound into bands of .diflerent frequency maybeaccomplished mechanically or electrically. Mechanical means consists inthe I adjustment of the volume of the reverberation changes andmodifications.

crophone in the enclosure; a remotely controlled chamber whereby theparticular chamber becomes responsive to frequencieswithin a certainrange. Adjustable chambers 88, 81, 68 are used for this urpose. They maybe so adjusted that and reverberation chambers of constant volume Thecontrol motors '28, 40 of the reverberation chambers are connected byleads 82, 83, 84 with controller 85, 86. All the potentiometers for thebranch lines and the motor control apparatus are placed on a controltable where an operator can manipulate them in accordance with'thedesired final eflect. Additional potentiometers 8l-may be providedbetween the microphones and the line 69. V

A more or less large number of reverberation chambers or enclosures maybe used for radio recording or broadcasting. The chambers 88. 61, 68,69, also 88, 61', 68', 69' may be connected in groups of a few as shown.in Fig. 5. each group containing several chambers. The microphonecircuits are connected with potentiometers 92 for regulating relativestrength of impulses from the individual chambers. A commonpotentiometer 94 may be provided for further adjustment of theindividual signals before they are passed into amplifiers 95, 96.

A modified acoustic reverberation chamber is shown in Fig. 6 comprisingan enclosure 98 provided at the'sides with bypass ducts 89 and I00 withshutters l0l, I02 which can be adjusted to any desired degree ofopening. The bypass ducts can be used to vary the volume of the chamber,and, also to divide the sound waves into several channels of diilerentlength thereby adding novel acoustic effects. a

In another modification shown in Fig. 7 the enclosure 103 is providedwith an additional chamber I04 at the side, having" ducts I 05 beingdirectly opened into the surrounding space and provided with shuttersI06. The open ducts modify the reverberation properties of the chamber.Movable piston-like members I 01'. may be also provided to vary thevolume of the extension chamber.

In combining several acoustic chambers as shown in Fig. 4, the controlscan be assembled in one place where an operator can manipulate contactpoints or switches arranged in the. form of 1 electric impulses.

a keyboard. A special music or other chart may be provided for guidingthe operator.

It will be understood that variou features and rinciples of each of theembodiments of the in- 7,

in the art after understanding the invention, that scope or theinvention, and it i intended there fore in the appended claims to coverall such What is claimed as new cured by Letters Patentis:

I claim as my invention: 7 1. A reverberation modulator comprising anenclosure having a wall made of a'flexible material; means to support aloud speaker and a mimotor at the enclosure; means to move said walls bythe motor in a transverse direction for varying the volume of theenclosure, and means for passing said flexible wall in a plurality .ofgenerally transverse directions to bring the various portions thereoffrom a gathered position as desired.

2. A reverberation modulator comprising a frame; walls movably supportedat avplurality of sides of the frame having a series of interchangeableportions of different reverberation roperties along their length; amotor at the enclosure; means to move the walls by the motor lengthwisefor placing portions or the walls with desired reverberation propertiesover the frame; and meansto support a loud speaker and a microphone inthe frame; said moving means serving to interchange portions of saidwalls to bring one portion out of operative relation with said loudspeaker and microphoneand to bring another portion into operativerelation with said loud speaker and microphone.

3. Means to control reverberation in sound transmission by radiocomprising a plurality of reverberation enclosures for loud speakers andmicrophones, each reverberation enclosure bei adapted to reproduce asound of a limited band of frequency difierent from the' frequencies ofthe other reverberation enclosures; means to combine the electricimpulses from different enclosures into a single channel; and means tomodulate the reverberation in different enclosures by varying physicalproperties of the enclosures.

4. Means to control reverberation in sound transmission by radiocomprising means to. convert sound into electric impulses; a pluralityof enclosures forming reverberation chambers; means to separate from theelectric impulses bands of selected frequencies and to direct the bandsinto the individua1 reverberation chambers; means to .convert theselected bands into sound in the reverberation chambers; means tomodulate the sound by varyin physical properties of the reverberationchambers; means to convert the modulated sounds into electric impulses;and means to combine the electric impulses from the reverberationchambers with the unmodified 5. Means to control sound transmissioncom-. prising a plurality of reverberation enclosures; means to converta sound into electric impulses of different frequencies; means toselectively reproand desired to be see position to an operative means;means: to individually vary the intensity 0! the electric impulses fromdifferent enclosures qualities and means move said movable set tointerchange said. portions to bring one portion into voperative relationwith said stationary wall portions and another portioncut of operativerelation, with said stationary wall portions, said chamber havingsubstantially constant volumetric characteristics during said change.

9. A reverberation modulator comprising a set otstationary wallportions,a set of movable wall diflerent frequency bands in differentreverbera- "ticn chambers; modulating the sound in the chambers byvarying by remote control-reverberation properties of thechambemiconverting' the sound in the chambers into electric impulses;in-

dividually modulating the impulses; and combining' the impulses fromdiflerent chambers into a single channel.

,7. A reverberation modulator comprising en- .closure means a wall ofwhich has interchangeportions, 'electrosc'nic conversion means carriedby one set, the various portions of the movable set having surfaces ofvarying sound'reflecting qualities. and power means Ioreflecting'accurate ,and measurable relative adjustment of said welland-said electrosonic means to interchange portions '01 said walliormingpart of said enclosure to bring a portion 01' said wall out ot operativerelationship' with said conversion means and to bring a .wallpcrtionhaving different reverberaable portions oi diflerent reverberationcharacteristics, electrosonic means, and 'means to im- I part relativemovement to said wall and said electrosonic means to bring saidelectrosonic means and one portion or said wall out of operativerelationship and to bring said electrosonic means and another portion oisaid wall into operative relationship.

8. Areverberationmodulator comprising a set or stationary wall portions,a set or movable wall 'portio'ns, 'electrcsonic conversion means'carrledby one set. the various portions of the movable 'set havingsuriaces orvarying sound reflecting tion' characteristics into operativerelationship with said conversion means.

10. A reverberation modulatorcomprising a set of stationary wallportions, a set ct movable wall portions, electrosonic conversion meanscarried by one set, the various portions of the movable set I havingsurfaces or varying sound reflecting qualities, and remote control means,to move said movable set relatively to said stationary set to removeone ot'the portions or said set and to bring into operative relationshipanother of the portions of said set;

v MAURICE PARISIER.

